The present invention relates to coatings compositions for thermoplastic and thermosetting plastic materials and the coated plastic articles.
Plastic materials such as thermoplastic olefin (TPO) have been developed which are useful in many applications, such as automobile parts and accessories, containers, household appliances, and other commercial items. It is often desirable to coat articles made from such plastic materials with organic coating compositions to decorate them or to protect the plastic materials from degradation when exposed to atmospheric weathering conditions such as sunlight, moisture, heat and cold. To achieve longer lasting and more durable parts, it is necessary for the coatings to be tightly adhered to the surface of the plastic.
Plastic substrates made from a variety of thermoplastic and thermosetting plastic materials have widely varying surface properties including surface tension, roughness, and flexibility, which make it difficult to achieve adequate adhesion of the organic coatings to such materials, particularly after aging or environmental exposure of the plastic materials. The problems are particularly difficult in automotive applications where in addition to the requirement that decorative and protective coatings adhere well to the plastic substrate, there are other requirements which are difficult to achieve. In respect to the utilization of thermoplastic polyolefin substrates, these requirements include a high degree of resistance of the finally coated part to organic solvents, particularly gasoline, and a high degree of resistance of any hardened coating to humidity.
A number of proposals have been made for overcoming the adhesion problem ranging from flame or corona pretreatments to the application of various primer compositions containing chlorinated polyolefins to the plastic polyolefin substrate. Some examples of chlorinated polyolefins for use in coating compositions can be found in U.S. Pat. Nos. 4,997,882; 5,319,032; and 5,397,602.
However, while such techniques have achieved a fair measure of success with respect to the adhesion problem, there remain various disadvantages such that the goal, for example, of achieving a desired combination of excellent adhesion, solvent resistance, particularly to gasoline, and humidity resistance in an advantageously economic manner has remained elusive.
It is an object of the present invention to provide a coating composition for use on thermoplastic polyolefin substrates that provides excellent adhesion, humidity resistance, and solvent resistance, particularly to gasoline.
It is another object of the present invention to provide a thermoplastic polyolefin article coated with the coating composition of this invention.